1. Field of the Invention
The present invention relates to an automotive anti-lock control system.
2. Discussion of Background Art
Conventionally, as automotive anti-lock control systems, there is known in general an anti-lock control system comprising a normally-opened electromagnetic valve provided along a connection line which connects a master cylinder for generating a brake fluid pressure through the operation of a brake pedal and a wheel brake and a normally-closed electromagnetic valve along a release line which connects a reservoir for reserving brake fluid and the wheel brake, wherein, when a wheel is about to be locked up, the normally-opened electromagnetic valve is put in a closed condition, whereas the normally-closed electromagnetic valve is put in an opened condition so that a brake fluid pressure built up at the wheel brake is released to the reservoir via the release line (a pressure decreasing mode), in addition, when the brake fluid pressure at the wheel brake is attempted to be held, both the normally-opened electromagnetic valve and the normally-closed electromagnetic valve are put in closed conditions so that the wheel brake is cut off from the connection line and the release line (a holding mode), and furthermore, when the risk of wheel lockup has disappeared, the normally-opened electromagnetic valve is put in the opened condition, whereas the normally-closed electromagnetic valve is put in the closed condition so that a brake pressure built up at the master cylinder is transmitted directly to the wheel brake via the connection line (a pressure increasing mode), whereby, as required, the braking force is adjusted and controlled so that the slip rate of the wheel does not exceed largely a predetermined value through automatic control of so-called pumping operations by selecting the modes in an alternative fashion.
Then, in this type of automotive anti-lock control system, during the so-called holding mode where the brake pressure at the wheel brake is held as it is, in order to keep the normally-opened electromagnetic valve in the closed condition, a current value corresponding to 100% of the rated current value is applied continuously (for example, refer to Patent Literature No. 1).
[Patent Literature No. 1]
JP-A-9-104335 (page 14, FIGS. 15, 16)
In the above conventional automotive anti-lock control system, while the current value corresponding to 100% of the rated current value is applied continuously to the normally-opened electromagnetic valve in the holding mode, this rated current value is a value determined based on such demands that the automotive anti-lock control system should be able to function appropriately even if the battery voltage value of the vehicle decreases and that the normally-opened electromagnetic valve should be able to be held in the closed condition in an ensured manner even if a pedal depressing pressure applied to the brake pedal by the driver becomes maximum, and therefore, applying the current value corresponding to 100% of the rated current value to the normally-opened electromagnetic valve in a normal usage means that a current more than required or excessive current is applied to the same valve.
Due to this, there are pointed out problems that consumed current is increased and that the response to a changeover to the pressure increasing mode(requiring the normally-opened electromagnetic value to be changed over from the closed condition to the opened condition) which tends to be executed following the holding mode is degraded.